Motor driven positioning apparatus with force-controlled shutoff switches

ABSTRACT

A drive gear is driven by a motor, the gear positioning the positioned member, such as a valve stem, with predetermined force against an obstruction, such as a valve seat. A torque sensing means is provided sensing excess torque applied by the motor to the gear to disconnect the motor. In the disclosed embodiment, the torque sensing element includes a cage swingable over a shaft and carrying, offset with respect to the shaft, a gear transmitting drive power from the motor to the positioned gear. The cage is restrained from swinging about the shaft by a spring; if the torque transmitted exceeds the restraining spring force, the cage will deflect, deflecting movement causing shut-off of the motor. To end-position the valve stem, spring-controlled frictional force is applied to the drive gear when a terminal position is reached causing axial excursion of the drive gear relative to its housing.

United States Patent Balz [4 Oct. 24, 1972 [541 MOTOR DRIVEN POSITIONINGAPPARATUS WITH FORCE- CONTROLLED SHUTOFF SWITCHES [72] Inventor: JurgenBalz, Heilbronn Neckar,

Germany [22] Filed: Jan. 13, 1971 [21] Appl. No.: 106,030

[30] Foreign Application Priority Data Sept. 12, 1970 Germany ..P 20 45249.7

[52] U.S.Cl. .......192/141,l92/142R,192/150, 251/134 [51] lnt.Cl...F16d7l/00,Fl6k31/04 [58] Field ofSearch....l92/150, 141, 142 R;251/134 [56] References Cited UNITED STATES PATENTS 2,208,119 7/1940Chandler ..192/150 1,702,479 2/1929 Moschetal. ..192/150' 2,407,5379/1946 Chapman .;....192/150X 3,115,791 12/1963 Dean ..74/785X FOREIGNPATENTS OR APPLICATIONS 1,547,154 10/1968 France ..25l/l34 380,3509/1932 GreatBritain ..25l/l34 Primary Examiner-Allan D. HerrmannAttorneyFlynn & Frishauf [5 7] ABSTRACT A drive gear is driven by amotor, the gear positioning the positioned member, such as a valve stem,with predetermined force against an obstruction, such as a valve seat. Atorque sensing means is provided Sensing excess torque applied by themotor to the gear to disconnect the motor. In the disclosed embodiment,the torque sensing element includes a cage swingable over a shaft andcarrying, offset with respect to the shaft, a gear transmitting drivepower from the motor to the positioned gear. The cage is restrained fromswinging about the shaft by a spring; if the torque transmitted exceedsthe restraining spring force, the cage will deflect, deflecting movementcausing shutoff of the motor. To end-position the valve stem,spring-controlled frictional force is applied to the drive gear when aterminal position is reached causing axial excursion of the drive gearrelative to its housing.

10 Claims, 4 Drawing Figures PATENTEI] BET 24 I972 Fig. 1

PATENTEU w 24 I97? I 3 .7 OD 085,

m 2 or 4 Fig. 2

3,700,085 sum 3 [1F 4 PATENTED um 24 1372 MOTOR DRIVEN POSITIONINGAPPARATUS WITH FORCE-CONTROLLED SHUTOFF SWITCHES CROSS REFERENCE TORELATED PATENTS U.S. Pats. Nos. 3,616,884and 3,647,038.

The present invention relates to a motor drive to position a member withpredetermined force against an obstruction, for example a valve memberin final valve opening, or closing positions. The valve member itself isconnected by means of a spindle with the motor drive, the spindletransmitting axial movement.

It has previously been proposed to position a valve member, suchas avalve shut-off element rigidly with a drive. When the positioning forceexceeds a predetermined value, the drive is to be disconnected. To thisend, a drive gear is located for limited axial movement, and maintainedin a centered, neutral position by a pair of springs pressing againstbearings located in the housing of the positioning apparatus. The drivegear can move longitudinally with respect to the bearings; the axialmovement, by the drive gear (or the bearings, respectively) then causeengagement of a friction member against the end face of the drive gear,to effect coupling of the friction member with the drive gear uponexcursion of the drive gear, or the bearings, as the end or terminalposition is being reached.

Motor drives of this type have previously been proposed see applicationsSer. 882,974 (Filed Dec. 8, 1969) now U.S. Pat. No. 3,616,884 (FiledJuly 20, l968) now US. Pat. No. 3,647,038. The apparatus disclosed inthe aforementioned applications has the advantage that the interruptionof power to the motor depends on the force of application of thepositioned member, here a valve element, to an obstruction, such as avalve housing. Operating practice has shown that the friction betweenthe spindle thread and the spindle nut, sliding thereon, is notnecessarily constant but rather can vary over a wide range. Thesevariations apparently arise due to differences in surface condition ofthe mutually engaging thread, caused by dirt, wear on the threads, andlubricating effectiveness, all of which greatly influence the finalfriction to be overcome by the motor drive. Tests taken during operatingconditions have shown that the friction may vary between about ,u.=0.02and p.=0.2, depending upon whether the friction is break-away friction,moving friction, and depending on the condition of the engaging threads.

The wide variations in friction between the threads require wide changesin the torque to be supplied to the drive wheel driving the spindle ofthe positioned element, for example a valve member. To provide foreffective force positioning in which the actual positioning force issubstantially constant, the drive therefor must be dimensioned to theworst condition, that is, the drive motor as well as the gearing betweenthe drive motor and the wheel driving the spindle must be of a sizecapable of transmitting torque to overcome the highest expectedfriction, to avoid damage or destruction of the drive elements. Thisleads to a substantial overdimensioning of these parts which, inpositioning drives having force applications in the order of tons, ishighly undesired, since, under normal conditions, the excessivedimensioning of the parts is not utilized. They do, however, requireadditional space, and are costly.

If the dimensioning of the positioning drive starts from a median designvalue of, for example, 11:0.1, then an exact positioningwith designpositioning force is ensured if the friction is below this limitingvalue. If, however, friction rises to po=0.2 due to external influences,then the torque to be applied over the drive gear is doubled in ordertoobtain a pure force-dependent final positioning. This overloads thedrive motor, as well as the gear elements; no effective protectionagainst such overload is available.

It'is an object of the present invention to provide a positioning drivein which the force of final positioning, exceeding a certain value,disconnects the drive, as above referred to; and which, additionally, isimproved in that an overloading of the drive motor, and any gearingbetween the drive motor and the final positioning gear is avoided.

SUBJECT MATTER OF THE PRESENT INVENTION terminal position.

In a preferred form of the invention, the torque sensing devicecomprises a swingable cage inwwhich a gear is retained, offset from theswing-axis of the cage; the gear is part of a gear train, and the cageis restrained from deflection away from a predetermined position by aspring. If the torque transmitted by the gear exceeds a predeterminedvalue, the cage will deflect against the spring, and the deflectingmovement of the cage is utilized to disconnect power to the drive motor.

The drive is smaller and the design values of the various elements canbe optimized in comparison to drives which are insensitive totransmitted torque. For normal conditions of friction in the drivethreads, the ordinary end-force positioning switching arrangement isused. lf, however, due to change of the friction conditions within thegearing, or the spindle thread and nut arrangement, the torque exceeds acertain value, the drive can be disconnected before damage can result.Thus, the force acting on the spindle is held within a wide normalrange, to effect disconnection of the motor when the final positioningforce has been reached. The force to be transmitted by the motor cannot,however, exceed a certain value so that the torque transmitted by thegearing remains within predetermined limits. This enables precisedimensioning of all parts of the drive, resulting in a good space factorand a drive of high efficiency. Additionally, the drive enables asimplification in number of parts and in the number of types of drivesto be stocked since it can be used as a pure torque-sensitive driveregardless of eventual output from the spindle requiring, in addition tothe torque sensing, a final end-switching arrangement depending onpositioning force.

In a preferred form, the arrangement is so made that a drive gear isprovided which, when the force acting on the spindle increases beyond amaximum value, is restrained from movement and, eventually,automatically blocked so that the drive gear wheel itself increases thetorque being transmitted, the switching mechanism then being operated bythe torque sensing arrangement.

The inventionwill be described by way of example with reference to theaccompanying drawings, wherein:

FIG. 1 is a side view of a positioning drive applied to a valve;

FIG. 2 is an axial cross-sectional view, with the valve omitted, andshowing the parts in greater detail;

FIG 3 is a top view taken along lines 3-3 of FIG. 2; and

FIG. 4 is a cross-sectional view taken along lines 4- 4 of FIG. 3.

A valve 1 has a movable valve member 2 connected to a spindle 3 which,by means of a slider 4, surrounding one of a pair of posts 5 isrestrained from rotation and movable lengthwise to open or close thevalve. The valve spindle 3 is held in a threaded nut 6, which is inthreaded engagement with a moving spindle 7, the spin- -dle 7 and nut 6forming ,a linearly movable positioning drive. Upon rotation of spindle7, nut 6 will move longitudinally, to convert the rotary motion of thespindle into longitudinal motion of the valve body 2.

A housing 8 is supported on the posts 5. Spindle 7 extends into thehousing 8 and is retained therein by means of a pair of ball bearings 9,10. Spindle 7 is formed with a cylindrical part 11, extending on bothsides of a main drive gear 12, fixed on the spindle 7. The two ballbearings 9, 10 are longitudinally slidable. A pair of essentiallyU-shaped'leaf springs 13 are inserted between the ball bearings 9, 10,see FIG. 4. The leaf springs tend to push the ball bearings 9, 10against shoulders 14, 15 formed at housing walls 16, 17. The ballbearings 9, 10, are guided radially by extension sleeves 18, 19 of thehousing wall. The cylindrical part 11 of spindle 7 has a pair of C-rings20, 21 bearing against the inner races of the ball bearings 9, 10. Apair of levers 22 are arranged in the region between the main gear 12and the inner races of ball bearings 9, 10. The central opening 23 oflevers 22 is just slightly larger than the outer diameter of cylindricalpart 11. Levers 22 are formed at their ends with notches 24 (see FIG. 3)which match with a rib 25 formed on the housing, to restrain the leversagainst rotation. The inner diameter of opening 23, and notch 24 holdthe levers in position without interfering with movement of the spindlecylinder 1 1. Levers 23 are arranged between a pair of elastic rings 24'which are so dimension that, if the spindle is not loaded, there is aslight axial distance between the drive wheel 12 and the rings, andbetween the inner race of ball bearings 9, 10 and the rings,respectively.

Spindle 7 and with it main drive gear 12 is driven by a motor 26 locatedon a housing 8, connected with a pinion 27. Pinion 27 is connected togear 12 by a gear train. The geartrain includes a shaft 28, parallel tospindle 7 and rotatably joumalled in the housing 8. Shaft 28 is broughtout of the housing. A pair of gears 29, 30, are freely rotatably mountedon the shaft 28. Gear 29 engages with pinion 27. Gear 30 engages withdrive wheel 12. The gears 29, 30 are, in turn, interconnected by a gear33. Gear 33 is located in a cage 31 which is swingably mounted aboutshaft 28, and capable of lateral excursion, that is, up or down in FIG.3.

Cage 31 supports shaft 32 on which the gear 33 is mounted. The cage 31is fixed to shaft 28, so that shaft 28 swings with the swinging motionof the cage 31. Shaft 28 additionally is formed with a lever 34 which,upon deflection of the shaft 28 from a center, or rest position operatesa pair of associated switches 35, 36 depending upon the direction ofdeflection.

Cage 31 may be formed in the general shape of a U- shaped bail, orframe. It is formed with a flat surface 37 which bears against a leafspring 38, secured at 39 in housing 8, for example by spot welding, by agroove, or any other suitable attachment means. Leaf spring 38 retainsthe cage 31 in the center, or neutral position illustrated in FIG. 3.Ifthe torque on the cage 31 exceeds a predetermined value, the cage 31will snap out of the central position shown in FIG. 3 and deflectlaterally, causing deflection of the shaft 28 and thus operation of thelimit switch.

Operation: Upon starting motor 26, spindle v7 is rotated over the geartrain formed by pinion 27, gears 29,33, 30 and main gear 12. Cage 31 isat the rest position retained as illustrated in FIG. 3. Elastic rings24' are freely movable in axial direction between the drive gear 12 andthe inner races of ball bearings 9, 10. Operating levers 22 are loose,and rotation of the spindle 11 is not impeded in any way. When theoperated member reaches the limit position at which it meets anobstruction, and specifically, as illustrated, when the valve member 2reaches the valve seat, an increasing axial force is applied to spindle7 which has as a result that drive wheel 12 will tend to move upwardly.Upon excursion of the drive wheel upwardly, the lower ball bearing 9 iscarried along by the C-ring 21, the upper ball bearing 10 itself bearingagainst the housing shoulder 16. Upon increasing excursion, the distancebetween the gear 12 and the inner races of the bearings 9,- 10 willdecrease until the elastic rings 24' on both sides of the operatinglevers 22, are compressed, thus forming a frictional engagement betweenthe drive wheel l2 and the two operating levers 22. Since the operatinglevers 22 are restrained from rotation by the engagement of notch 24with housing rib 25, a drag force is applied to main gear 12 which willtend to stop rotation of the gear 12. The value of the axial forceacting on spindle 7 which causes blocking of the drive wheel 12 isdetermined by the strength of springs 13 which counteract the axialforce applied against the spindle. As soon as the drive wheel 12 iseffectively restrained from rotation, the torque transmitted over thegear 33 and shaft 32', mounted on the, cage 31, will increase. This willtend to deflect cage 31 from the position shown in FIG. 3, againsttheforce of leaf spring 38. When the torque reaches a limiting value,thedeflecting force will be so great that the cage will snap out of theneutral position and cause deflection of the cage, with the deflectionof shaft 28 and engagement of lever 34 with one or the other of theswitches 35, 36 which disconnect the drive motor.

The aforementioned operation describes the sequence under normalcircumstances, that is, when the friction p. between the spindle 7 andthe spindle nut 6 is so small that a deflection of the cage 3.1 willonly occur when the drive wheel is constrained from further movement bythe terminal seating force. .Under the aforementioned unusual operatingconditions, however, the friction p. in the drive strain formed ofthreads 6, 7, may increase substantially. The torque to be transmittedby the pinion 27 over gearing 29,33, 30, to drive main gear 12 will thenbe so great that the cage 31 will deflect from its neutral position(FIG. 3) and thus disconnect the motor. The value of the torque upondeflection of cage 31 is determined by the strength of leaf spring 38;it can be adjusted by suitable dimensioning of the leaf spring, bypre-biasing or other suitable means not shown and well known in the art.Switches 35, 36 can be connected not only to disconnect the motor butalso to operate an alarm circuit; they can, for example, be additionallyinterconnected with limit switches determining the position of thespindle 7 so that seating with force less than the design force can beindicated, for example, to show to operating personnel that prematureoperation of the switches 35, 36 occurred and that the positioningapparatus needs cleanin g or maintenance.

The embodiment as described illustrates a drive gear 12 which is securedto spindle 7, on which a nut 6 is threaded, restrained against rotation.Of course, the position of nut and spindle can be reversed, so that thespindle connected to the valve member is restrained from rotation, andthe nut is driven and connected to gear 12. Various other changes andmodifications may be made, for example as required by specific uses andapplications, within the inventive concept.

I claim:

1. Motor driven positioning apparatus to place a positioned member withpredetermined force against an obstruction, having switch means 34, 36disconnecting the motor 26 when the force transmitted by the drive tothe positioned member 2 exceeds a predetermined value comprisin ahousing 8;

a drive gear 12 coupled to the positioned member;

means 9, 10; 14, l5; 16, 17, 18, 19; 20, 21 retaining said drive gear insaid housing and permitting axial excursion of said drive gear withrespect to said retaining means;

spring means 12 maintaining said gear in neutral,

central position with respect to the permitted excursion relative tosaid retaining means; locking means 22, 24, located to be frictionallyengageable by said drive gear upon relative axial excursion thereof toapply a drag force on said drive gear, said drag force increasing withincreasing axial excursion of the drive gear 12 and locking the drivegear upon full permitted excursion of said drive gear against the forceof said spring means 13;

gear means 27, 29, 33, interconnecting said motor 26 and said drive gear12;

and means 28, 31, 38 sensing torque transmitted by said gear means andactuating said switch means to interrupt power to said motor uponsensing of torque beyond a predetermined value and independently of theaxial force acting on the drive gear.

2. Positioning apparatus according to claim 1 wherein;

said torque sensing means includes a displaceable element 31 beingdisplaced upon transmission of torque beyond said predetermined value,displacementqf said element actuating sgid switch eans. 3. Positioningapparatus accor mg to calm 1 wherein said locking means 22, 24, 25comprises a pair of levers 22;

means 24, 25 restraining said levers from rotation; and wherein saiddrive gear retaining means includes a pair of bearings 9, 10 mounted insaid housing for relative axial excursion with respect thereof; saidbearings, upon said relative axial excursion, providing axial engagementforces between said levers, said bearings, and said drive gear. 4.Positioning apparatus according to claim 1 wherein said sensing meansincludes a cage 3l'and a shaft 28 secured to the cage, the cage andshaft being swingably mounted in said housing;

a gear 33 rotatably mounted in said cage on an axis remote from theshaft 28;

and said gear means comprises a gear 29 interconnecting the motor andthe gear 33 on the cage and a gear 30 engaging the drive gear 12 and thegear on the cage 33, said gear on the cage 33 coupling the gear 29driven by the motor and the gear 30 driving the drive gear 12 togetherto provide a deflecting force to the shaft 28 upon transmission oftorque from the motor to the drive gear.

5. Positioning apparatus according to claim 4 including resilient means37, 38 restraining said shaft 28 from deflection and holding said shaftin a rest position, said resilient means permitting deflection of saidshaft when the torque transmitted over gear means exceeds apredetermined value;

said switch means being located to be actuated upon deflection of saidshaft.

6. Positioning apparatus according to claim 4 including resilient means37, 38 holding said shaft 28 in a rest position and restraining saidshaft from deflection, said resilient means and said shaft beingmutually engageable by a snap-action coupling having a predeterminedsnap force.

7. Positioning apparatus according to claim 4 including a flat surface37 rotatable with said shaft;

and spring means 38 mounted in said housing and bearing against andengaging said flat surface.

8. Positioning apparatus according to claim 4 wherein the shaft 28extends through the housing for said apparatus, said switch means beinglocated on said housing to be engageable by said shaft upon deflectionthereof.

9. Positioning apparatus according to claim 1 including a threadedspindle 7 driven by said drive gear 12 and an engaging threaded member 6in engagement with the threads on said spindle and restrained fromrotation, said threaded member being coupled to the element beingpositioned.

10. Positioning apparatus according to claim 9 in combination with avalve, wherein said positioned member is a valve element movablelongitudinally within the valve, against a valve seat, the predeterminedforce being the seating force of said valve element.

1. Motor driven positioning apparatus to place a positioned member withpredetermined force against an obstruction, having switch means 34, 36disconnecting the motor 26 when the force transmitted by the drive tothe positioned member 2 exceeds a predetermined value comprising ahousing 8; a drive gear 12 coupled to the positioned member; means 9,10; 14, 15; 16, 17, 18, 19; 20, 21 retaining said drive gear in saidhousing and permitting axial excursion of said drive gear with respectto said retaining means; spring means 12 maintaining said gear inneutral, central position with respect to the permitted excursionrelative to said retaining means; locking means 22, 24, 25 located to befrictionally engageable by said drive gear upon relative axial excursionthereof to apply a drag force on said drive gear, said drag forceincreasing with increasing axial excursion of the drive gear 12 andlocking the drive gear upon full permitted excursion of said drive gearagainst the force of said spring means 13; gear means 27, 29, 33, 30interconnecting said motor 26 and said drive gear 12; and means 28, 31,38 sensing torque transmitted by said gear means and actuating saidswitch means to interrupt power to said motor upon sensing of torquebeyond a predetermined value and independently of the axial force actingon the drive gear.
 2. Positioning apparatus according to claim 1wherein; said torque sensing means includes a displaceable element 31being displaced upon transmission of torque beyond said predeterminedvalue, displacement of said element actuating said switch means. 3.Positioning apparatus according to claim 1 wherein said locking means22, 24, 25 comprises a pair of levers 22; means 24, 25 restraining saidlevers from rotation; and wherein said drive gear retaining meansincludes a pair of bearings 9, 10 mounted in said housing for relativeaxial excursion with respect thereof; said bearings, upon said relativeaxial excursion, providing axial engagement forces between said levers,said bearings, and said drive gear.
 4. Positioning apparatus accordingto claim 1 wherein said sensing means includes a cage 31 and a shaft 28secured to the cage, the cage and shaft being swingably mounted in saidhousing; a gear 33 rotatably mounted in said cage on an axis remote fromthe shaft 28; and said gear means comprises a gear 29 interconnectingthe motor and the gear 33 on the cage and a gear 30 engaging the drivegear 12 and the gear on the cage 33, said gear on the cage 33 couplingthe gear 29 driven by the motor and the gear 30 driving the drive gear12 together to provide a deflecting force to the shaft 28 upontransmission of torque from the motor to the drive gear.
 5. Positioningapparatus according to claim 4 including resilient means 37, 38restraining said shaft 28 from deflection and holding said shaft in arest position, said resilient means permitting deflection of said shaftwhen the torque transmitted over gear means exceeds a predeterminedvalue; said switch means being located to be actuated upon deflection ofsaid shaft.
 6. Positioning apparatus according to claim 4 includingresilient means 37, 38 holding said shaft 28 in a rest position andrestraining said shaft from deflection, said resilient means and saidshaft being mutually engageable by a snap-action coupling having apredetermined snap force.
 7. Positioning apparatus according to claim 4inclUding a flat surface 37 rotatable with said shaft; and spring means38 mounted in said housing and bearing against and engaging said flatsurface.
 8. Positioning apparatus according to claim 4 wherein the shaft28 extends through the housing for said apparatus, said switch meansbeing located on said housing to be engageable by said shaft upondeflection thereof.
 9. Positioning apparatus according to claim 1including a threaded spindle 7 driven by said drive gear 12 and anengaging threaded member 6 in engagement with the threads on saidspindle and restrained from rotation, said threaded member being coupledto the element being positioned.
 10. Positioning apparatus according toclaim 9 in combination with a valve, wherein said positioned member is avalve element movable longitudinally within the valve, against a valveseat, the predetermined force being the seating force of said valveelement.